UV-absorbing monomer and polymers thereof

ABSTRACT

UV absorbing compounds, susceptible to free-radical polymerization, of the formula   &lt;IMAGE&gt;   wherein R is alkyl having from 4 to 12 carbon atoms of which not more than 6 are present in a linear chain, and in particular 2-(2&#39;-hydroxy-3&#39;-methacrylamidomethyl-5&#39;-tert-octylphenyl)benzotriazole, and polymers thereof.

This application is a division of application Ser. No. 787,660, filedOct. 16, 1985, now U.S. Pat. No. 4,612,358.

The present invention relates to certain polymerizable ultravioletabsorbing compounds of the formula ##STR2## and to ultraviolet absorbingpolymers prepared therefrom. More in particular, the invention relatesto those compounds wherein R¹ is methyl and R is (C₄ -C₁₂)-alkyl havingno more than six carbon atoms in a linear (unbranched) chain.

The monomeric compounds of the invention and their polymers have astrongly absorbing effect for ultraviolet radiation of wavelengths up toabout 400 nm. Such radiation has a damaging effect on many importantengineering plastics. To protect plastics sensitive to ultravioletradiation, polymerizable UV absorbers are incorporated in them or areapplied, in the form of their polymers, as a protective layer to thesurface of these plastics.

Many compounds of the above formula where R' is a hydrogen atom areknown from U.S. Pat. No. 3,399,173. These compounds are derivatives ofacrylamide. Polymers of these compounds are relatively soft and theirVicat softening point is so low that they are usually not suitable foruse as engineering plastics. Their copolymers with methacrylic monomersare considerably softer or have a lower Vicat softening point than dothe homopolymers of the methacrylic monomers or of styrene.

From the same patent, other derivatives of the aforementionedmethacrylamides are also known wherein R' is methyl and R is eithermethyl or long chain alkyl, for example, n-octyl or n-dodecyl. Thesepolymerizable UV absorbers are also unsuitable for the production ofultraviolet absorbing plastics comprising copolymers of methacrylicmonomers or of styrene since the compound where R is methyl does notsufficiently dissolve in methacrylic monomers and in styrene and thecompounds with long chain groups R have the same softening effect as theacrylamide derivatives mentioned earlier, where R' is hydrogen.

Surprisingly, it has now been found that compounds of the aforementionedformula wherein R' is methyl and R is alkyl having from 4 to 12 carbonatoms of which not more than 6 are arranged in a continuous unbranched(linear) chain are readily soluble in most unsaturated vinyl orvinylidene monomers, and particularly in methacrylic monomers and instyrene, and, moreover, do not have a pronounced softening effect oncopolymers with these monomers. Even with relatively high contents ofunits derived from the UV absorbers of the invention, these copolymerspossess valuable synthetic resin properties.

The undesirable softening effect of the prior art UV absorbers seems tooccur whenever, in the compounds of the formula, R' is methyl, R isalkyl having more than 5 unbranched carbon atoms, for example a n-octylor n-dodecyl group, or R contains such a group.

The preferred compounds of the invention are those which have from 6 to12, and more particularly from 8 to 10 carbon atoms in the group R. Thetert.-octyl derivative having a group R of the structure ##STR3## hasproved particularly advantageous. Further examples of the new UVabsorbers are compounds wherein R is tert.-butyl, tert.-amyl, n-hexyl,cyclohexyl, or triisobutyl. The advantage offered by the new UVabsorbers is apparent from a comparison of the Vicat softening points(VSP) of various copolymers (with molecular weights ranging from 100 to100,000, as determined by gel permeation chromatography) of 80 weightpercent methyl methacrylate and 20 weight percent of a compound of theaforementioned formula:

    ______________________________________                                                 Compound of formula (I)                                                                      VSP (DIN 53460)                                                (R)      (R')      (°C.)                                      ______________________________________                                        In accordance                                                                            tert.-Octyl                                                                              Methyl    108                                           with the invention                                                            For comparison:                                                                          Polymethyl           108-109                                                  methacrylate                                                                  n-Octyl    Methyl    102                                                      tert.-Octyl                                                                              Hydrogen   80                                                      n-Octyl    Hydrogen   73                                           ______________________________________                                    

The new UV absorbers can be prepared by processes analogous to those ofthe prior art compounds. The reaction of N-methylolacrylamide or itsalkyl esters with 2-(2'-hydroxy-5'-alkylphenyl)benzotriazoles of theformula ##STR4## wherein R has the meaning given earlier and R" ishydrogen or alkyl preferably containing from 1 to 4 carbon atoms, ispreferred. When acid catalyzed with concentrated sulfuric acid as thereaction medium, the reaction proceeds in the temperature range from 0°C. to 50° C. with good yields.

The new UV absorbers lend themselves to the production of UV absorbingcopolymers. To this end, they are conventionally exposed, when inadmixture with other vinyl or vinylidene monomers, to the action of aninitiator which generates free radicals. Preferred vinyl or vinylidenemonomers are styrene and methacrylic monomers. The latter includemethacrylonitrile and monomers with the group CH₂ ═C(CH₃)--CO--, andparticularly alkyl esters of methacrylic acid which preferably containfrom 1 to 4 carbon atoms in the alkyl group. Copolymers withhydroxyalkyl methacrylates also possess interesting technicalproperties. Methyl methacrylate is particularly preferred. Thesepreferred monomers usually represent 50 weight percent or more of thecopolymer. Suitable further comonomers are acrylonitrile, esters ofacrylic acid, vinyl esters, vinyl halides and, in minor amounts, specialmonomers having particular functional groups.

The but slightly softening effect of the new UV absorbers is manifestespecially in copolymers which have a Vicat softening point of over 100°C. and which include more than 3 weight percent of the new UV absorbers.

The amount of these UV absorbers incorporated in the copolymers willdepend on the intended effect. When the copolymer serves as aUV-protective layer for a plastic that is sensitive to ultravioletradiation, then polymers containing more than 10 weight percent, and inparticular from 20 to 60 weight percent, of the UV absorbing monomerwill be suitable. If, however, the plastic itself is to be protected,then the proportion of the UV absorber will generally be less than 10weight percent, and usually less than 1 percent. As a rule, a proportionof UV absorber of less than 0.05 weight percent will not provideadequate protection.

A better understanding of the invention and its many advantages will behad by referring to the following specific examples, given by way ofillustration.

EXAMPLES

(A) Preparation of a polymerizable UV absorber

900 ml of 96-98 percent sulfuric acid are introduced into a 2-litermultinecked flask equipped with stirrer and internal thermometer and322.1 g (1 mole) of 2-(2-hydroxy-5-tert-octylphenyl)benzotriazole("Cyasorb UV 5411", a product of American Cyanamid Co.) is dissolvedtherein. A yellow solution forms. The latter is held at 15° C. to 20° C.and mixed in portions with 120.4 g (1.05 moles) of 98 percenthydroxymethylmethacrylamide. On completion of this addition, thereaction mixture is allowed to react further for 2.5 hr. at roomtemperature. The mixture is then dripped with vigorous stirring intoabout 3 liters of ice water. The pale yellow reaction productprecipitates. The precipitate is filtered off by suction and washedneutral with a saturated aqueous sodium bicarbonate solution. Thesubstance is then washed with distilled water, vigorously filtered offby suction, and dissolved in about 2 liters of methylene chloride. Theorganic phase is successively extracted from 2 to 3 times with distilledwater, dried with Na₂ SO₄, filtered, mixed with 0.015 g of2,2,6,6-tetramethylpiperidine N-oxide radical (a polymerizationinhibitor) and concentrated so far as possible in a rotary evaporatorunder a water jet vacuum at not more than 50° C. The remaining substanceis suspended in hexane and filtered off by suction. To remove the slightyellow coloration of the crystals, the product is mixed with a littlemethanol and then filtered off by suction. The crystals are rewashedwith hexane and the product is then dried to constant weight at roomtemperature. Yield: 355 g (81.1% of theory) of2-(2'-hydroxy-3'-methacrylamidomethyl-5'-tert-octylphenyl)benzotriazole.

    ______________________________________                                        Analysis of reaction product:                                                          % C         % H    % N                                               ______________________________________                                        Calculated 71.4          7.6    13.3                                          Found      71.2          7.6    13.3                                          ______________________________________                                    

(B) Preparation of bulk polymers

20 parts of the compound prepared as described under (A) are dissolvedin 80 parts of weight of methyl methacrylate (MMA) with stirring andheating to 50° C. 0.1 part of dilauroyl peroxide and 0.4 part of dodecylmercaptan are added. The mixture is filtered and, after degasifying in avacuum, is filled into a foil bag which is closed with the exclusion ofair. For polymerization of the mixture, the foil bag is placed for 20hours in a water bath at 50° C. and for 8 hours in a heating cabinet at100° C. In the Table which follows, the polymer so obtained isdesignated as "I".

A mixture of 99.5 parts by weight of methyl methacrylate and 0.5 part ofthe UV absorber prepared as described under (A) is prepared in the samemanner. The resulting polymer is designated "II".

For comparison, two further bulk polymers "III" and "IV" are produed inthe same manner, except that in place of the compound prepared asdescribed under (A), wherein R represents tert-octyl, the knownanalogous compound with R being n-octyl is used. As may be seen from thefollowing Table, the polymers so produced have a significantly lowerVicat softening point (VSP).

                  TABLE                                                           ______________________________________                                                                          Reduced                                          Proportion                                                                              Proportion                                                                              UV absorber                                                                            viscosity                                                                            VSP                                  No.  MMA, (%)  (%)       (R)      (ml/g) (°C.)                         ______________________________________                                        I    80        20        tert-Octyl                                                                             45     108                                  II   99.5      0.5       tert-Octyl                                                                             50     109                                  III  80        20        n-Octyl  40     102                                  IV   99.5      0.5       n-Octyl  50     106                                  ______________________________________                                    

(C) Preparation of a bead polymer

A mixture of 250 parts by weight of the polymerizable UV absorberprepared as described under (A) and 250 parts of methyl methacrylate,2.5 parts of dilauroyl peroxide, and 1.5 parts of n-dodecyl mercaptanare added at 75° C. with stirring to 1000 parts by weight of water phasecontaining 0.2 percent (based on the water phase) of aluminum hydroxideas dispersant and, for improvement of the dispersant action, 5 percent(based on the aluminum hydroxide) of a sodium (C₁₄ -C₁₆)alkyl sulfonate,present in a 2-liter round-neck flask equipped with reflux condenser,thermometer, and stirrer, and suspended to form droplets. After apolymerization time of 60 minutes at 78°-80° C. and 60 minutes at84°-86° C., the bead polymer is washed with water on a nutsch filter anddried for about 20 hours at 50° C.

The copolymer is obtained in a yield of 99 percent. The average particlesize is 100 microns. The reduced viscosity of the polymer is 44 ml/g andits Vicat softening point is 100° C.

For comparison, a bead polymer is prepared under the same conditionsusing a corresponding amount of2-(2'-hydroxy-3'-methacrylamidomethyl-5'-n-octylphenyl)-benzotriazole inplace of the tert-octylphenyl derivative of the invention. The reducedviscosity of the bead polymer is 60 ml/g and its Vicat softening pointis 82° C.

We claim:
 1. A compound of the formula ##STR5## wherein R is alkylhaving from 4 to 12 carbon atoms not more than 6 of which are present inan unbranched chain.
 2. A compound as in claim 1 which is2-(2'-Hydroxy-3'-methacrylamidomethyl-5'-tert-octylphenyl)benzotriazole.